Additive manufacturing (AM), also known as solid freeform fabrication or 3D printing, refers to a manufacturing process in which three-dimensional objects are built up from successive dispensing of raw material (e.g., powders, liquids, suspensions, or molten solids) into two-dimensional layers. In contrast, traditional machining techniques involve subtractive processes in which articles are cut out from a stock material (e.g., a block of wood, plastic or metal).
A variety of additive processes can be used in additive manufacturing. Some methods melt or soften material to produce layers, e.g., selective laser melting (SLM) or direct metal laser sintering (DMLS), selective laser sintering (SLS), fused deposition modeling (FDM). Some methods cure liquid materials using different technologies, e.g., stereolithography (SLA). Some systems place binder materials onto layers of feed materials, e.g., powder, and use energy sources to cure the binder materials to bond loose powder particles together.
Some dry powder additive manufacturing apparatuses, such as binder-jetting 3D printers, can produce parts in a variety of materials. A typical binder jetting additive manufacturing process includes spreading a first uniform layer of powder across the platform. The powder particles can be of metal, ceramics, sand, plastic, a mixture of different materials, etc. The additive manufacturing apparatus then deposits binder materials onto the layer of powder at locations corresponding to a layer of the object to be fabricated. An energy source is used to cure the binder materials in order to bond powder particles together. After the binder material has been cured in the layer, the apparatus then spreads a second uniform layer of powder on top of the first layer, and repeats the binder depositing and curing steps. Once the apparatus finishes spreading all layers, a three-dimensional “green” part is formed within the pool of loose powder. The part is “green” in that the main constituent, i.e., the material provided by the powder, is held together by the binder material, and has not yet been sintered or fired to solidify the powder into a solid mass of material. The green part is formed of powder glued together by cured binder agents, and has a vertical spatial resolution equal to the thickness of each layer of powder. The loose powder particles can be recycled and stored for the next print. Depending on the type of powder particles, the green part may serve as the final product, or it may need to go through additional post-processing steps, such as annealing or sintering, hot isostatic pressing, etc., to form the final product.